How can a team finish fifth in a 14-team league, and still be crowned champions? That question could be answered at Old Trafford next Saturday, after Leeds Rhinos stunned Warrington in a thrilling play-off semi-final at the Halliwell Jones Stadium on Friday night to secure their sixth Grand Final appearance in eight seasons.

Warrington had finished top of the table, 13 points clear of Leeds who have had, statistically, their worst season since 2001. The Wolves even chose the Rhinos as their semi-final opposition under Super League's controversial Club Call innovation, although as the only other option were Wigan, the champions, that decision was taken with reluctance rather than relish.

But whereas Leeds, having lost 11 of their 27 league fixtures and drawn another, have timed their run to perfection – Friday's win was their fifth in a row since they emerged with huge credit from Wembley defeat by Wigan in the Challenge Cup final – Warrington's consistency throughout the summer meant nothing as their season was ended by a first defeat in 12 league matches.

Given the circumstances, the dignity of the Wolves coach, Tony Smith, in defeat was remarkable. He made a point of shaking the hand of Steve Ganson, the referee who had awarded the penalty that allowed a typically nerveless Kevin Sinfield to secure the Rhinos' 26-24 win with less than two minutes remaining – a brave, and correct, decision for which Ganson and his touch-judge, James Child, deserve credit after a difficult few weeks for Super League's match officials.

Smith had no complaints, at least in public, about the play-off system, even though Wigan and Huddersfield, who finished below the Wolves in the table, have enjoyed the luxury of a second chance, whereas Warrington's first defeat proved terminal. Did he regret playing safe by choosing to play Leeds, the lowest-ranked team, rather than gambling that Wigan might be tired with only five days to recover from last Sunday's victory over the Catalan Dragons?

"I regret the fact that we have to make a choice," he said. "As for picking the wrong team, we picked the lowest-ranked team, and I don't know that anybody else would have done too much differently."

The system may be manifestly unfair, as before Friday Leeds had lost seven and won one of eight fixtures against the teams who finished above them. But Super League's policy-makers will point to Friday night's drama and argue that the end justifies the means. They can also claim that Leeds are more legitimate Grand Finalists than the New Zealand Warriors, who finished sixth in the National Rugby League and were thrashed in their first play-off fixture in Brisbane – but clung on to record consecutive victories in Sydney and Melbourne to set up morning's showdown with Manly in a run that has lifted league from out of the long shadow cast over the southern hemisphere by the other code's World Cup.

Certainly the Rhinos were worthy winners at Warrington, and the major contributions made by Danny McGuire and Jamie Peacock provided both an explanation for the team's slump into midtable, and a possible vindication for the play-offs. They returned in late April, but it is only since mid-summer that these two stalwarts of the three consecutive Grand Final victories over St Helens from 2007-2009 have recaptured their best form.

Peacock's individual battle with Adrian Morley, the Warrington captain with whom he has packed down in so many internationals, was a compelling subplot of the drama. But one of the most crucial and thrilling moments among many in the second half was McGuire's ability to support a scampering break by his old half-back partner Rob Burrow, and then to hold off the Warrington cover just long enough for Ryan Hall to arrive to collect a lobbed pass and score his second try.

McGuire's effort was all the more admirable as moments earlier he had been hobbling with what looked like a recurrence of the hamstring problems that have occasionally troubled him since his return. The ball-playing stand-off is a formidable competitor. He suffered his knee injury in hugely controversial circumstances after playing a key role in an equally breathless Leeds win at Wigan in the first round of last season's play-offs, and was therefore a frustrated spectator, with Peacock, as the Warriors gained their revenge at Headingley two weeks later to deny the Rhinos a place at Old Trafford.

It would therefore be churlish to begrudge McGuire and so many of his Leeds team-mates this unexpected Grand Final appearance, whatever the reservations about the manner in which it has been secured.